Project Summary Glycogen is a normal branched polymer of glucose that acts as a reserve of glucose units, to be used for anabolism or as a source of energy. Abnormal glycogen metabolism is associated with some generalized metabolic disorders, most notably type 2 diabetes and insulin resistance, but in addition a number of individual genetic glycogen storage diseases (GSDs) or glycogenoses have been identified. In these, mutations in genes impacting glycogen metabolism result in abnormal glycogen deposits in a variety of tissues, often with serious and even fatal consequences. No truly effective treatments are available for the most serious disorders. Genetic depletion of glycogen levels has recently been shown to have efficacy in alleviating the pathology in a mouse model of Pompe disease. The main premise for this proposal is that suppression of glycogen accumulation is a promising therapeutic approach to combat glycogenoses in general and Pompe disease in particular. Aim 1: Identification of small molecule inhibitors of glycogen synthase. We will search for active site and allosteric site inhibitors of glycogen synthase by high-throughput screens using novel assays. Lead compounds will form the basis to develop focused libraries of chemically related molecules to enhance both potency and biological efficacy. Positives from the above screens will be confirmed by more extensive enzyme kinetic study and promising candidates evaluated in model cell systems and then at the whole animal level. Aim 2: Medicinal chemistry optimization. Compounds identified in Aim 1 (and Aim 3) will be evaluated for chemical properties and synthetic tractability, refined by purchase and/or the synthesis of focused libraries to develop improved compounds. Aim 3: Cell-based analyses of effectors of glycogen accumulation. We have developed novel assays to monitor cellular glycogen accumulation in cells. The assays will be applied to evaluate and validate any candidate glycogen synthase inhibitors identified in Aim 1 as well as an alternative way to screen compound libraries to identify novel inhibitors. Aim 4: Testing inhibitors of glycogen accumulation in mouse models of Pompe disease. Compounds identified in Aims 1 - 3 that show most promise will be tested in mice for toxicology and pharmacokinetics. Suitable compounds will then be administered to Pompe mice to assess their effects on glycogen overaccumulation, cardiac hypertrophy and locomotor impairment associated with the disease. In the future, we can test compounds with other mouse models of glycogenoses. Even one new effective drug would be of major importance for Pompe patients and possibly patients with other glycogen storage diseases.